1. Field of the Invention
The present invention relates to a fluid transport system that has a built-in pump for use in a wide variety of fields of air conditioning machines, refrigerators, air conditioners, oxygen water purifiers, combustors and so on, and a method therefor.
2. Description of the Related Art
Recently, there have been increasing needs for oil-free dry pumps in various fields. The dry pump is defined as a vacuum pump that can perform exhaustion with its outlet port being kept connected to the atmosphere using neither oil nor liquid at the gas passage of the pump. The dry pump is a mechanical vacuum pump of a new type, which has been developed first in Japan in the late 1980's and which has become rapidly widespread mainly in the semiconductor industry.
There have recently been growing demands for improving the vacuum pumps for semiconductor manufacturing processes in order to cope with higher integration density and finer structures. The demands mainly include the contents of 1) obtaining a high ultimate vacuum pressure, 2) cleanness, 3) easy maintenance and 4) small size and compactness. In order to respond to the demands, dry vacuum pumps for roughing have been widely used for the purpose of obtaining a cleaner vacuum in place of oil-sealed rotary vacuum pumps, which have been conventionally used. A number of types of pumps have been developed and put to practical use, where such pumps include positive displacement types of a screw type, a claw type, a scroll type, a multistage root type and so on as well as a kinetic type of a turbo type.
FIG. 16 shows a dry vacuum pump of a thread groove type (a kind of screw type), which is a kind of a conventional positive displacement vacuum pump (roughing vacuum pump).
FIG. 16 illustrates a housing 101, a first rotary shaft 102, a second rotary shaft 103, and cylindrical rotors 104 and 105 which are connected to the first and second rotary shafts 102 and 103, respectively. Thread grooves 106 and 107 are formed on the outer peripheral portions of the rotors 104 and 105, respectively, and by meshing the recess portion of one thread groove with the protruding portion of the other thread groove, a hermetic space is produced between them. If the rotors 104 and 105 rotate, the hermetic space then shifts from the suction side to the discharge side in accordance with the rotation, exerting a sucking action and a discharge action.
In the vacuum pump of the thread groove type of FIG. 16, synchronous rotation of the two rotors 104 and 105 is achieved by timing gears 110a and 110b. That is, the rotation of the motor 108 is transmitted from a driving gear 109a to an intermediate gear 109b and is transmitted to one gear 110b of the timing gears that are provided on the shafts of both rotors 104 and 105 and meshed with each other. The rotation angle phases of both the rotors 104 and 105 are adjusted by the meshing engagement of these two timing gears 110a and 110b. FIG. 16 also illustrates rolling bearings 113a, 113b and 114a, 114b, which support the first rotary shaft 102 and the second rotary shaft 103, respectively.
FIG. 16 also illustrates a built-in oil pump 115 at the end portion of the driving gear 109b, an oil pan 116 in a lowermost portion of the pump, oil 117, a suction chamber 118, a mechanical seal 119, and a fluid transfer chamber 120.
FIG. 17 shows a turbo type dry vacuum pump, which is a kind of a conventional kinetic vacuum pump.
FIG. 17 illustrates a rotor 200 located on the rotary side, a stator 201 located on the stationary side, a downstream side pump 202 that is called the vortex flow component and formed between the rotor 200 and the stator 201, an upstream side pump 203 called the centrifugal component, and an upper casing 204 that houses the rotor 200 and the stator 201. FIG. 17 also illustrates a rotary shaft 205 connected to the rotor 200, ball bearings 206a and 206b, a high-frequency motor rotor 207, a stator 208 of the motor rotor 207, an inlet port 209, an outlet port 210, an oil cooler 211, a lower casing 212, an intermediate casing 213, and a seal portion 214 provided between the intermediate casing 213 and the rotary shaft 205.
In the above-mentioned dry pump, a turbine wheel of the vortex flow component pump that is capable of obtaining a high compression ratio in a viscous flow is arranged on the outlet port side connected to the atmosphere, while a centrifugal component pump that operates as a molecular drag pump in a molecular flow is arranged on the inlet port side. A diaphragm type dry vacuum pump, which is a kind a of positive displacement type vacuum pump, is widely used as a means for performing suction and transport of fluid in a clean state. The diaphragm type pump is used as a comparatively small displacement means for transporting fluid since the pump is able to perform suction, compression, and discharge of fluid in a hermetic space completely isolated from the drive sections of the motor, bearings and so on.
Recently, there have been increasing needs for clean vacuum transport in the fields of, for example, foods, pharmaceuticals, agriculture, and healthcare equipment besides the aforementioned semiconductor processes. For example, a technology for enriching oxygen in the air by using a polymer gas separation membrane (oxygen enriching membrane) has become widespread and utilized for medical treatment, air conditioning in a room, or industrial uses related to combustion and biotechnology besides the aforementioned foods, pharmaceuticals, agriculture, and healthcare equipment.
A known oxygen enriching apparatus, as shown by example in FIG. 18, is provided with an oxygen enriching module 301 for selectively separating oxygen from the atmosphere, a vacuum pump 302 for obtaining oxygen-enriched air by reducing the internal pressure of the module 301, an air blower fan (means) 303 for supplying air into the module 301, and a dehumidifying unit 304 for removing steam and moisture from the oxygen-enriched air.
The oxygen enriching module 301 is provided with, for example, an oxygen enriching membrane of a composite material constructed mainly of polydimethylsiloxane and has a permeability rate of oxygen that is faster than that of nitrogen and a much faster permeability rate of steam. The vacuum pump (reduced pressure pump) 302 is used for reducing the internal pressure of the oxygen enriching module 301, providing a pressure difference between the inside and the outside of the membrane and obtaining oxygen-enriched air. The air blower fan 303 operates to form airflow, supply air to the oxygen enriching module 301 and remove steam from the periphery of the dehumidifying unit 304. Moreover, the dehumidifying unit 304 is provided on the discharge side of the vacuum pump 302 and is constructed so that it internally has a passage of oxygen-enriched air and is arranged in an airflow produced by the air blower means 303.
The oxygen enriching module is a well-known material which is capable of obtaining the oxygen-enriched air by utilizing the principle that oxygen, which is located on the atmospheric side and dissolved in the surface of the membrane, is diffused and moved inside the membrane and separated from the membrane surface on the reduced pressure side by providing a pressure difference between both surfaces of the separation membrane. For example, under the condition of a reduced pressure level of −560 mmHg (−74.5 KPa), the normal air of N2: 79% and O2: 21% becomes the oxygen-enriched air of N2: 68% and O2: 32% by permeating through the oxygen enriching module. The module has the characteristics of an easily obtainable large flow rate, a stabilized oxygen concentration, a light weight, a low consumption of power and so on.
As the uses of the oxygen enriching apparatus, there is, for example, an oxygen inhaler for medical use, healthcare use and first aid use. As a method for obtaining oxygen gas, it is a general practice to fill a portable container with oxygen gas separated by low-temperature separation, and there is demanded a low-cost portable oxygen inhaler which makes best use of the features of the oxygen enriching module and is able to be filled with oxygen handily and easily without frequency limitation.
Moreover, it is possible to conversely make the aforementioned hermetic space nitrogen rich by extracting oxygen O2 from the atmosphere in the hermetic space by utilizing the principle of this oxygen enriching membrane.
This nitrogen enriching apparatus has a use for food preservation to prevent the oxidation of foods. For example, there is an earnest demand for forming a nitrogen-enriched space in a refrigerator to maintain the freshness of foods of, for example, vegetable, fish, and meat for a long time.
As to other uses, uses have been developed for countermeasures against dioxin in processing industrial waste by oxygen-enriched high-temperature combustion, CO2 reduction combustion for combustion with a reduced amount of fuel, an air purifier and an air conditioner intended for the creation of an oxygen-enriched room, and so on.
In the case where the aforementioned system has been constructed for the purpose of creating an oxygen-enriched or nitrogen-enriched air, the common subjects required for the vacuum pump (or pressurizing pump), which has been the important key unit of the system, has been, for example, as follows.
(1) A displacement Q is required to be about 0.5 to 6 l/min, and a vacuum pressure P at the operating point is required to be, for example, −600 mmHg to −400 mmHg (−80 KPa to −53 KPa).
(2) The structure is required to be as simple and compact as possible.
(3) Low vibration and silence are required.
(4) A long operating life is required.
Furthermore, in addition to the above-mentioned requirements (1) through (4), in the case of an oxygen enriching apparatus for medical treatment and healthcare or a nitrogen enriching apparatus for food preservation, the vacuum pump is required to be:
(5) completely oil free.
That is, the use of machine oil is kept at a distance from any portion that communicates with the exhaustion space of the pump. When a vacuum pump is applied to an air conditioning machine, air conditioner, or the like, the level of cleanness required for the vacuum pump is considered to roughly correspond to the above although the level is less significant than in the case of medical treatment, healthcare, and foods.
A vacuum pump, which concurrently satisfies the aforementioned requirements (1) through (4) or (1) through (5), cannot be found conventionally. If such a vacuum pump is materialized, it is expected that the pump will be an initiator for rapidly popularizing the oxygen enriching apparatus.
Assuming the dry vacuum pump that is widespread mainly in the semiconductor industry is replaced with a vacuum pump of the aforementioned oxygen enriching apparatus following the driving principle and the fundamental structure of the dry vacuum pump, there have been the following issues that have not been able to be easily solved. One of the issues is the relation between displacement and an ultimate vacuum pressure.
In the case of the positive displacement pump, the relation between displacement and efficiency or between displacement and the ultimate vacuum pressure is not linear. The smaller the displacement, the further the efficiency and the ultimate vacuum pressure becomes extremely reduced. The reason for the above is that the processing and assembling accuracies of the members that constitute the pump cannot be proportionally improved even if the pump body and the components are reduced in size. Taking the case of the thread groove type dry vacuum pump, which is the aforementioned positive displacement type vacuum pump, as an example, a ratio of occupation of the total amount of internal leak of gas that passes through a gap between the two rotors 104 and 105 or a gap between the rotor and the housing 101 with respect to the closed transport space increases extremely as the displacement reduces. When the speed of the rotor rotation is increased in order to reduce the influence of the internal leak as far as possible, there emerges new issues of an increase in the amount of generated heat and a reduction in the operating life of a seal in a mechanical seal portion 119 that accompanies a mechanical sliding friction, an increase in torque, vibrations of the timing gear portions 110a and 110b, and so on.
In other words, it is not easy to replace the vacuum pump for a semiconductor, which normally has a displacement of not smaller than 500 l/min, with a clean pump that can obtain a pressure P of −600 mmHg to −400 mmHg (−80 KPa to −53 KPa) with a displacement of about 1/100 while scaling down the dimensions and weight in correspondence with the displacement and maintaining a low consumption of power, following the fundamental structure of the vacuum pump.
Another issue is to make the pump free of oil. The thread groove type dry vacuum pump, which is the aforementioned positive displacement type vacuum pump, has a construction in which a gap of normally tens of micrometers can be kept at the portion where the two thread groove rotors 104 and 105 mesh with each other or between the rotor and the casing 101 in FIG. 16. Since a relative phase relation between the two rotors is kept by the timing gears 110a and 110b, there is no mechanical slide portion in the fluid transport space, and clean exhaustion can be achieved. However, oil lubrication is required for the one pair of timing gears and bearings. Oil 117 for this lubrication is sucked from an oil pan 116 located in a lowermost portion of the pump by the oil pump and is supplied to the bearings and the gears via an oil filter. A mechanical seal 119 is provided so as to prevent the oil from flowing into the fluid transfer chamber 120 that houses the thread groove rotor and to prevent the reactive gas transported inside the fluid transfer chamber 120 from intruding into the oil storage space. Other 2-rotor pump types of, for example, the root type, the Wankel type, and the claw type have roughly similar fundamental structures in the portions that need lubrication.
The turbo type dry vacuum pump (FIG. 17), which is the aforementioned kinetic vacuum pump, is driven to rotate normally at a velocity of several tens of thousands of revolutions per minute. In the case of the pump of this type, the timing gear employed in the positive displacement type is not necessary, but oil lubrication to the ball bearing portions is still indispensable. Moreover, a seal means for isolation between the portions that need lubrication with oil and the clean fluid transport space is also necessary.
That is, in the dry pump for semiconductor processes, regarded as oil free, the fluid transport space is merely isolated from the oil-rich space by the mechanical seal means, and there is no change from the conventional pump with regard to the fact that oil for lubrication is the indispensable condition of the pump drive section.
Here, the propriety of reducing the size of the pump constructed as described above by scaling down and the application thereof to clean pumps for healthcare, medical equipment and foods or, for example, an oxygen inhaler for supplying oxygen to a person, an oxygen water purifier for producing oxygen water by bubbling oxygen in a water tank, food preservation for preventing the oxidation of foods by making a refrigerator room internally nitrogen rich, and so on are considered. Even if the fluid transport space can be kept physically completely clean, the fact that the oil-rich space filled with machine oil exists in the neighborhood via a mechanical seal cannot be sensuously unacceptable in an aspect.
In other words, it is extremely difficult to replace the vacuum pump for a semiconductor, which normally has a displacement of not smaller than 500 l/min, with a clean pump for foods, pharmaceuticals, medical treatment, healthcare equipment, and so on to keep a displacement of about 1/100 following the fundamental structure of the vacuum pump.
The diaphragm type dry vacuum pump that is the positive displacement type vacuum pump, which can suck and discharge fluid in a clean hermetic space completely isolated from the drive sections of motors, bearings, and so on, has therefore been the only pump which can be capable of resolving the aforementioned issues. Moreover, the pump is good at exhaustion at a comparatively small flow rate. However, the pump has had the following drawbacks.
(1) Vibration and noise are large.
(2) The pump body is increased in size due to poor pump efficiency.
(3) Operating life is short because of fatigue due to repetitive stress application to the diaphragm membrane.
(4) A low ultimate vacuum pressure cannot be obtained.
The noise of the item (1) is dominated by a pulsation sound of air discharged by intermittent driving. The poor efficiency of the item (2) is attributed to the positive displacement vacuum pump driving principle that the power of the piston in either the suction or discharge stroke does not work as a regenerating action. The item (3) becomes a fatal drawback in supposed application to, for example, a consumer use refrigerator, which must continuously operate for many years regardless of day and night.
In short, a pump, which is able to perform clean exhaustion completely free of oil similar to the diaphragm type pump and to remove the aforementioned drawbacks of the diaphragm type, does not exist conventionally. Accordingly, the appearance of a new pump is necessary and expected.
In view of the aforementioned conventional problems, an object of the present invention is to provide a noncontact completely oil-free fluid transport system by supporting a viscosity pump with a hydrodynamic gas bearing and a method therefor.
In order to achieve the aforementioned object, the fluid transport system of the present invention is constituted of a fluid transport system, which includes a pump constructed of a rotor housed in a housing, a bearing for supporting the rotation of this rotor, a fluid transfer chamber formed of the rotor and the housing, fluid inlet and outlet ports that are formed at the housing and communicate with the fluid transfer chamber, a motor for rotatively driving the rotor, and a transport groove that is formed at a relative displacement interface between the rotor and the housing and exerts a fluid pumping action.